Determining Dialog States for Language Models

ABSTRACT

Systems, methods, devices, and other techniques are described herein for determining dialog states that correspond to voice inputs and for biasing a language model based on the determined dialog states. In some implementations, a method includes receiving, at a computing system, audio data that indicates a voice input and determining a particular dialog state, from among a plurality of dialog states, which corresponds to the voice input. A set of n-grams can be identified that are associated with the particular dialog state that corresponds to the voice input. In response to identifying the set of n-grams that are associated with the particular dialog state that corresponds to the voice input, a language model can be biased by adjusting probability scores that the language model indicates for n-grams in the set of n-grams. The voice input can be transcribed using the adjusted language model.

TECHNICAL FIELD

This document generally relates to computer-based speech recognition,and more particularly to biasing language models based on dialog states.

BACKGROUND

Increasingly, computing devices are provided with the capability toreceive spoken user input in addition to or alternatively to typedinput. Voice assistant applications, for example, may determine tasks toperform on a device based on multi-stage dialogs of prompts and spokenresponses between the voice assistant and a user. Likewise, web browsersand other applications on some devices are arranged to receive voiceinputs in form fields to obviate the need for a user to type input intothe fields. Voice inputs provided by a user to a computing device may beprocessed by a speech recognizer. The speech recognizer may includecomponents such as an acoustic model and a language model that arecollectively configured to transcribe voice inputs to text.

SUMMARY

Systems, methods, devices, and other techniques are described herein fordetermining dialog states that correspond to voice inputs and forbiasing a language model based on the determined dialog states. In someimplementations, a speech recognition system may automatically learn aset of dialog states and a respective language model biasing mode foreach respective dialog state. The dialog states and biasing modes may bedetermined without being predefined by a user.

Some implementations of the subject matter described herein include acomputer-implemented method. The method can include receiving, at acomputing system, audio data that indicates a voice input anddetermining a particular dialog state, from among a plurality of dialogstates, which corresponds to the voice input. A set of n-grams can beidentified that are associated with the particular dialog state thatcorresponds to the voice input. The set of n-grams can be associatedwith the particular dialog state based at least on n-grams in the set ofn-grams occurring frequently in historical voice inputs that correspondto the dialog state. In response to identifying the set of n-grams thatare associated with the particular dialog state that corresponds to thevoice input, a language model can be biased by adjusting probabilityscores that the language model indicates for n-grams in the set ofn-grams. The voice input can be transcribed using the adjusted languagemodel.

These and other implementations can optionally include one or more ofthe following features.

The plurality of dialog states can respectively indicate a plurality ofstages of user voice interactions with a computing device that pertainto a particular task.

The computing system may receive a second voice input and may determinea second particular dialog state, from among the plurality of dialogstates, which corresponds to the second voice input. A second set ofn-grams can be identified that are associated with the second particulardialog state that corresponds to the second voice input. The second setof n-grams can be different than the set of n-grams that are associatedwith the particular dialog state that corresponds to the voice input.

Determining the particular dialog state that corresponds to the voiceinput can include: identifying a second particular dialog state, fromamong the plurality of dialog states, that corresponds to a second voiceinput that preceded the voice input, wherein the voice input and thesecond voice input each pertains to a same task; and determining theparticular dialog state that corresponds to the voice input based ondata that indicates one or more dialog states among the plurality ofdialog states that are likely to occur after the second particulardialog state.

Determining the particular dialog state that corresponds to the voiceinput can include generating a transcription of the voice input anddetermining a match between one or more n-grams that occur in thetranscription of the voice input and one or more n-grams in the set ofn-grams that are associated with the particular dialog state.

Determining the match can include determining a semantic relationshipbetween the one or more n-grams that occur in the transcription of thevoice input and the one or more n-grams in the set of n-grams that areassociated with the particular dialog state.

Data can be received that indicates a context associated with the voiceinput. Determining the particular dialog state that corresponds to thevoice input can include identifying the particular dialog state based onthe context associated with the voice input.

The context associated with the voice input can include data thatcharacterizes a display of a user interface at a computing device atwhich the voice input was received at a time that the voice input wasreceived. Identifying the particular dialog state based on the contextassociated with the voice input can include identifying the particulardialog state based on the data that characterizes the display of theuser interface at the computing device at which the voice input wasreceived at the time the voice input was received.

An application identifier can be received at the computing system thatindicates an application to which the voice input was directed at acomputing device. The plurality of dialog states can pertain to anapplication-specific task for the application to which the voice inputwas directed.

Some implementations of the subject matter described herein includeanother computer-implemented method. The method can include obtaining aplurality of transcriptions of voice inputs that correspond to differentstates in a multi-state dialog. For each transcription among theplurality of transcriptions, a set of n-grams that occur in thetranscription can be identified. A plurality of groups of transcriptionscan be generated by assigning to each of the groups a respective subsetof transcriptions among the plurality of transcriptions for which theidentified sets of n-grams are determined to be related. Based on theplurality of groups of transcriptions, a model can be determined thatindicates a plurality of dialog states that occur in the multi-statedialog and a respective set of n-grams associated with each dialogstate. The determined model can be provided to bias a language modelthat is used in a speech recognition process.

These and other implementations can optionally include one or more ofthe following features.

A plurality of dialog states can be determined by assigning each of thegroups in the plurality of groups of transcriptions to a respectivedialog state among the plurality of dialog states such that each of theplurality of dialog states corresponds to a respective subset of thegroups of transcriptions and the respective subsets of the groups oftransactions for each of the plurality of dialog states are differentfrom each other. The respective set of n-grams associated with eachdialog state among the plurality of dialog states can be selected basedon the identified sets of n-grams that occur in transcriptions in therespective subset of the groups of transcriptions that correspond to thedialog state.

A first dialog state among the plurality of dialog states can correspondto a first subset of the groups of transcriptions that includes two ormore of the groups of transcriptions.

Generating the plurality of groups of transcriptions can include forminggroups of transcriptions that are determined be semantically similar toeach other.

The computing system can receive data that indicates an order that atleast some of the voice inputs were submitted in the multi-state dialog.Based at least on the data that indicates the order that the at leastsome of the voice inputs were submitted in the multi-state dialog, asequence of the dialog states in the plurality of dialog states can bedetermined. The sequence information can indicate, for each respectivedialog state, one or more other dialog states that follow the respectivedialog state or one or more other dialog states that precede therespective dialog state.

The plurality of transcriptions of voice inputs can include, for eachrespective dialog state among the plurality of dialog states in themulti-state dialog, multiple transcriptions of voice inputs thatcorrespond to the respective dialog state among the plurality of dialogstates.

The computing system can receive data that indicates respective contextsassociated with the voice inputs that correspond to at least some of theplurality of transcriptions. Generating the plurality of groups oftranscriptions can include grouping transcriptions further based on thedata that indicates the respective contexts associated with the voiceinputs that correspond to the at least some of the plurality oftranscriptions.

The respective context associated with a first voice input thatcorresponds to a first transcription among the plurality oftranscriptions can include data that characterizes a display of a userinterface at a computing device at which the first voice input wasreceived at the time that the first voice input was received.

Some implementations of the subject matter described herein can includea computing system. The computing system may include one or moreprocessors and one or more computer-readable media. Thecomputer-readable media store instructions that, when executed, causeperformance of operations that include receiving audio data thatindicates a voice input; determining a particular dialog state, fromamong a plurality of dialog states, that corresponds to the voice input;identifying a set of n-grams that are associated with the particulardialog state that corresponds to the voice input, wherein the set ofn-grams are associated with the particular dialog state based at leaston n-grams in the set of n-grams occurring frequently in historicalvoice inputs that correspond to the dialog state; in response toidentifying the set of n-grams that are associated with the particulardialog state that corresponds to the voice input, adjusting a languagemodel by increasing probability scores indicated by the language modelof n-grams in the set of n-grams; and transcribing the voice input usingthe adjusted language model.

In some implementations, the techniques described herein may, in certaininstances, realize one or more of the following advantages. A speechrecognizer may generate more accurate transcriptions of voice inputsusing a language model that is biased based on dialog states determinedto correspond to the voice inputs. Moreover, the dialog states thatoccur in a human-machine dialog may be autonomously determined by acomputing system so that application developers need not keep track ofdialog states in their respective applications or provide dialog stateidentifiers to a speech recognition system that transcribes voice inputsfor the respective applications. In some implementations, a computingsystem can determine respective sets of n-grams associated with aplurality of dialog states based on analysis of historical voice inputsand transcriptions. The sets of n-grams may be used to bias a languagemodel in different ways based on which dialog state is detected for agiven transcription request. Beneficially, in some implementations,these techniques may eliminate the need for application developers tomanually provide the sets of n-grams associated with each dialog stateto a speech recognition system.

DESCRIPTION OF DRAWINGS

FIG. 1 depicts a conceptual system-flow diagram of an example processfor transcribing a voice input to text using a language model that hasbeen biased based on an identified dialog state associated with thevoice input.

FIG. 2 depicts a second conceptual system-flow diagram of an exampleprocess for transcribing a voice input to text using a biased languagemodel. The language model represented in FIG. 2 is biased based onn-grams associated with a particular dialog state that the systemidentifies based on one or more dialog states that preceded the voiceinput.

FIG. 3 is a graph that represents an example dialog state-flow model.The graph includes nodes that correspond to a plurality of dialog statesand directional edges that correspond to transitions between particulardialog states.

FIG. 4 is a flowchart of an example process for determining dialogstates and respective sets of n-grams associated with the dialog statesbased on analysis of historical voice input or transcription records.

FIGS. 5A and 5B are conceptual diagrams of techniques for mergingsimilar groups of transcriptions to form a final set of groups thatcorrespond to dialog states determined to occur in a dialog.

FIG. 6 is a flowchart of an example process for performing speechrecognition using a biased language model that is selected based on adialog state associated with the recognized voice input.

FIG. 7 shows examples of a computing device and a mobile computingdevice that may be used to perform the computer-implemented methods andother techniques described herein.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

This document generally describes systems, methods, devices, and othertechniques for identifying and using dialog states to bias languagemodels, such as language models that may be used by a speech recognizerto transcribe a voice input to text. Techniques are described, forexample, for automatically determining dialog states and n-grams withoutan application or application developer explicitly identifying thedialog state or n-grams associated with a given voice inputtranscription request. These techniques and others are described infurther detail with respect to the figures.

Referring to FIG. 1, a conceptual diagram is shown of a computing systemperforming an example process 100 of transcribing a voice input 110 totext using a language model 120 that has been biased based on anidentified dialog state that corresponds to the voice input 110. Thesystem includes a speech recognizer 102 in communication with a userdevice 108. The user device 108 may generally be any type of computingdevice that is capable of detecting voice inputs from a user. Forexample, the user device 108 may be a desktop computer, a notebookcomputer, a smartphone, a tablet computing device, a television or othermultimedia device, or a wearable computing device such as a smartwatch.The user device 108 may include a microphone that detects voice input,and software and circuitry (e.g., an analog-to-digital converter) thatconverts the voice input to digital audio data.

In some implementations, the speech recognizer 102 may be operated onone or more computers that are remote from the user device 108. Forexample, the speech recognizer 102 may provide a cloud-based speechrecognition service that transcribes voice inputs from many differentuser devices in communication with the speech recognizer 102 over one ormore networks (e.g., the Internet). In this way, computing resources atthe respective user devices may be conserved due to the speechrecognition tasks being offloaded to remote servers with potentiallymuch greater computing power. In some implementations, the speechrecognizer 102 may be provided locally on the user device 108 so as toenable speech recognition capabilities even when the user device 108 isoffline and a network connection is unavailable.

The process 100 begins when a user 106 provides a voice input 110 to theuser's device 108. Before speaking, the user 106 may have activated amode on the device 108 that enables the device 108 to detect voiceinputs and to communicate with the speech recognizer 102 to generate atranscription of detected speech. In the example represented in FIG. 1,the user 106 has spoken the phrase “pepperoni and mushroom.” The phrasemay be spoken in the context of a multi-stage dialog that the user isengaged in with an application on the device 108 to place an order witha pizza restaurant. For example, the user 106 may select options for hisor her pizza order by completing a form presented in a user interface(e.g., a presentation of a web page or native application on the device108) that includes a collection of input fields (e.g., text fields,drop-down menus, or radio button selectors) for receiving the user'sinput. In some implementations, the device 108 may allow the user 106 toprovide input into each of the fields using different input mechanismssuch as typing or voice inputs. With typed input, the user 106 maydirectly input text into the various fields through a keyboard, whereaswith voice inputs, the user 106 dictates the text that is to be providedinto the various fields as voice inputs that are converted to text. Insome implementations, the user 106 may conduct a dialog with a voiceassistant on the device 108 in which the device 108 prompts the user 106to provide voice inputs in response to a series of questions presentedvisually and/or aurally to the user 106 (e.g., “What size pizza wouldyou like to order?”, “Which toppings would you like on your pizza?”,“Would you like to add any sides?”).

At operation A (104), upon receiving the voice input 110, the device 108generates a request 112 for the speech recognizer 102 to transcribe thevoice input 110 to text. If the speech recognizer 102 is remote from theuser device 108, the transcription request 112 can be transmitted over anetwork to the speech recognizer 102. The request 112 may include one ormore components. Generally, the request will include the digital audiodata for the voice input 110. In some implementations, the request 112may further include context data, an application identifier, a dialogidentifier, a dialog state identifier, or a combination of two or moreof these. In some implementations, the request 112 may include only thedigital audio for the voice input 110 without additional context data,an application identifier, a dialog identifier, or a dialog stateidentifier.

The context data in the request 112 may generally include any data otherthan the audio data for the voice input 110 which the speech recognizer102 may use to determine a transcription. Some types of context data mayindicate a condition or state of the user device 108 at or near a timethat the voice input 108 was detected by the device 108. As describedfurther below, examples of context data include user accountinformation, anonymized user profile information (e.g., gender, age,browsing history data, data indicating previous queries submitted on thedevice 108), location information, and a screen signature (i.e., datathat indicates content displayed by the device 108 at or near a timewhen the voice input 110 was detected by the device 108). In someimplementations, the application identifier, dialog identifier, anddialog state identifier may be considered as special types of contextdata, but are discussed separately here by way of example.

An application identifier may be included in the request 112 to identifya particular application, among multiple applications capable of beingidentified by the speech recognizer 102, to which the voice input 110was directed. In some implementations, the speech recognizer 102 maystore different sets of dialog states or other language model biasingdata for different applications, and the application identifier can beused by the speech recognizer 102 to determine the appropriate set ofdialog states to use in transcribing the voice input 110. For example,the speech recognizer 102 may store a first set of dialog states andlanguage model biasing data for the pizza ordering application, and adifferent second set of dialog states and language model biasing datafor a banking application. By including the application identifier inthe request 112, the speech recognizer 102 can recognize that therequest 112 pertains to the pizza ordering application, for example.Accordingly, the first set of dialog states and language modelingbiasing data associated with the pizza ordering application can beselected for use in transcribing the voice input 110.

In some implementations, the request 112 to transcribe the voice input110 may include a dialog identifier. The dialog identifier may indicatea particular dialog, among multiple dialogs, to which the transcriptionrequest 112 pertains. In some implementations, the dialog identifier maybe used to distinguish among multiple dialogs provided in a singleapplication. For example, the primary dialog of the pizza orderingapplication may be a dialog for submitting a pizza order. But theapplication may further provide other dialogs that allow the user tointeract with the application in different ways, such as a dialog thatallows a user to submit customer feedback or a dialog that allows a userto adjust account settings. The speech recognizer 102 may use the dialogidentifier to distinguish the possible dialogs from each other andselect appropriate models and parameters for biasing the language modeland transcribing the vice input 110.

In some implementations, the request 112 to transcribe the voice input110 may include a dialog state identifier. The dialog state identifiermay indicate a particular dialog state, among multiple dialog states ina given dialog, to which the transcription request 112 pertains. Adialog state is generally a representation of one or more stages of adialog in which a user provides voice inputs to a computing device. Thestages of the dialog can constitute a series of user interactionsrelated to a particular task or activity. For example, a dialog for theactivity of ordering a pizza may include stages at which respectivevoice inputs are received for selecting a pizza size, selectingtoppings, specifying a delivery address, and providing paymentinformation. A dialog state may be assigned to each of the stages of theactivity, and some dialog states may be assigned to multiple stages. Thedialog state identifier may indicate which of the states the voice input110 is directed to. In some implementations, the dialog state identifiermay be a true indication of a dialog state that is used by the speechrecognizer 102 to determine a manner for biasing the language model 120.In some implementations, a dialog state “hint” (e.g., in the form of aninteger) may be provided that indicates the dialog stage or the device'sestimate of the true dialog state. The speech recognizer 102 may trust adialog state hint or may use other data (e.g., context data, dialogstate history data) to verify whether the hint is accurate.

At operation B (114), the speech recognizer 102 processes the request112 to determine a dialog state associated with the request 112 (andthus associated with the voice input 110). In some implementations, thespeech recognizer 102 uses information contained in the request 112other than the audio data for the voice input 110 to determine thedialog state associated with the request 112. For example, if therequest 112 included an application identifier, a dialog identifier, anda dialog state identifier, then all three pieces of information could beused to determine the dialog state. The application identifier mayidentify a particular application that is associated with a set of oneor more dialogs. The dialog identifier may identify which of thesedialogs the request 112 is related to, and the dialog state identifiermay identify which dialog state within the identified dialog that therequest 112 is related to. A dialog state may be determined in someimplementations even if none or less than all three of these pieces ofinformation are provided to the speech recognizer 102.

In some implementations, the speech recognizer 102 may use other typesof context data to select a dialog state. For example, the request 112may include a hash value that characterizes the user interface displayedon the device 108 at or near a time that the voice input 110 wasprovided to the device 108 (i.e., a screen signature). Subsequently, thespeech recognizer 102 may compare the hash value received in the request112 to predetermined hash values that are associated with differentdialog states. A particular dialog state associated with a predeterminedhash value that matches the hash value received in the request 112 maythen be selected as the dialog state that the voice input 110 andrequest 112 are determined to correspond to. In some implementations,the selection of a dialog state may be based on two or more types ofcontext data (e.g., a screen signature, a dialog state hint, and alocation indicator that indicates a geographic location of the device108 when the voice input 110 was detected). In some implementations, thespeech recognizer 102 may select the dialog state by using a classifierthat outputs a predicted dialog state based on multiple signalsincluding multiple types of context data. The classifier may be rulebased or may be trained by machine-learning processes (e.g., a neuralnetwork).

In the example of FIG. 1, a representation of a data structure 116 isdepicted that correlates each of a plurality of dialog states withrespective context data and a respective set of one or more n-grams(e.g., language model biasing data). In particular, five dialog statesare shown that correspond to different stages in the pizza orderingdialog. For example, dialog state ‘1’ relates to the user's preferencefor a delivery or carry-out option, whereas dialog state ‘2’ relates tothe user's preference for a crust type and dialog state ‘3’ relates tothe user's preference for pizza toppings. In some implementations, adialog may include respective prompts at multiple different stages ofthe dialog that elicit similar responses from users. Each of thedifferent prompts may be associated with different context data, but thespeech recognizer 102 may have merged the similar prompts and responsesinto a single dialog state. For example, a pizza ordering applicationmay include a first prompt that asks the user 106 which toppings toinclude on the pizza and a second prompt that asks the user 106 if he orshe would like to add additional toppings at a discounted price. Thedevice 108 may provide a context value (e.g., dialog state identifier)of ‘1’ in the request 112 for the first prompt and may provide a contextvalue of ‘7’ in the request 112 for the second prompt. But because ofthe similarity among voice inputs responsive to each of these prompts,the speech recognizer 102 may maintain a single dialog state thatcorresponds to both prompts.

The data structure 116 identifies a respective set of one or moren-grams that are associated with each dialog state. The set of n-gramsassociated with a given dialog state generally indicate words, phrases,numbers, or other language units (i.e., n-grams) that frequently occurin voice inputs that have been determined to correspond to given dialogstate. For example, the data structure 116 identifies the n-grams“credit,” “pay,” “dollars,” “cents,” “in-store,” and “cash” as termsthat are likely to be uttered by a user in dialog state ‘5’, whichrelates to payment options for a pizza order. In some implementations,the respective n-grams assigned to each of the dialog states may bedetermined by the speech recognizer 102 based on analysis of results ofprevious transcription requests. For example, the speech recognizer 102(or another computing system) may log transcriptions of voice inputsfrom many different users over a period of time. A set of most popularterms (n-grams) that occur in the voice input transcriptions may then bedetermined and correlated with a dialog state. As such, there may be noneed for an application developer to provide the speech recognizer 102with sets of n-grams to associate with each dialog state. Rather, thespeech recognizer 102 may determine the sets of n-grams automatically byanalysis of historical transcription results. In some implementations,the set of n-grams associated with a given dialog state may include acombination of n-grams determined automatically without input from anapplication developer along with other n-grams that are specified by theapplication developer.

At operation C (118), the process 100 uses the set of n-grams associatedwith the selected dialog state to bias a language model 120 used by thespeech recognizer 102 to transcribe the voice input 110 to text.Generally, the language model 120 is configured to determine likelihoods(e.g., probabilities) that a language sequence represents an accuratetranscription of a voice input. For example, the language model 120 mayprocess a sequence of phonemes or other speech features generated by anacoustic model of the speech recognizer 102 to determine one or morecandidate transcriptions of the voice input 110. The language model 120may assign a probability to each of the candidate transcriptionsindicating a likelihood that the respective candidate transcription isan accurate transcription of the voice input. The top n candidatetranscriptions may then be returned to the user device 108 astranscription results, where n is a predetermined integer (e.g., 1, 2,3, 4, or more).

In some implementations, the language model 120 may determine theprobability for a candidate transcription based on probability data thatindicates how frequently different sequences of terms occur in one ormore corpora of language data. For example, the language model 120 mayassign a higher score to a transcription of “three blind mice” than“tree blind mice” because the former language sequence occurs morefrequently in a corpus of search queries than does the latter. In someimplementations, the language model 120 may be an n-gram language modelthat uses conditional probabilities to successively predict terms in alanguage sequence based on n or n−1 preceding terms in the sequence,where n is a predetermined integer (e.g., 1, 2, 3, 4, or more).

The speech recognizer 102 may bias the language model 120 so as toincrease or decrease the likelihood that a transcription result for thevoice input 110 includes n-grams from the set of n-grams associated withthe selected dialog state. In some implementations, the language model120 may be biased to favor candidate transcriptions that include n-gramsfrom the set of n-grams assigned to the selected dialog state. Forexample, the bar chart 122 in FIG. 1 shows a probability “boost” appliedto each of the n-grams associated with the selected dialog state (3),which relates to pizza toppings. Thus, whereas an unbiased languagemodel may assign a probability score of 0.20 to the candidatetranscription “pepperoni and mushroom”, the biased language model mayassign a probability score of 0.85, thus indicating a high likelihoodthat the candidate transcription accurately represents the content ofthe user's voice input 110.

In some implementations, even though probability data stored by thelanguage model 120 may be increased with respect to a set of n-gramsassociated with a selected dialog state, the biased language model 120may still be capable of generating transcriptions that do not includen-grams within the selected set (or that at least include one or moren-grams outside of the selected set). However, the likelihood ofgenerating a transcription with the biased language model 120 that doesnot include n-grams from the selected set of n-grams may be diminishedas compared to the likelihood of generating a transcription with theunbiased language model that does not include such n-grams. In someimplementations, the language model 120 may be biased by decreasingprobabilities associated with n-grams for a selected dialog state. Insome implementations, a given dialog state may be associated with afirst set of n-grams that have increased probabilities in the biasedlanguage model 120 and a second set of n-grams that have decreasedprobabilities in the biased language model 120.

At operation D (124), the speech recognizer 102 uses the biased languagemodel 120 to determine one or more transcription results for the voiceinput 110. In some implementations, a top-ranked transcription result126 (e.g., “pepperoni and mushroom”), which the biased language model120 indicates is likely the most accurate transcription of the voiceinput 110, can be selected and returned to the user device 108 inresponse to the request 112 (operation E (128)). The user device 108 maythen input the transcription result as text into a form field, forexample.

FIG. 2 is a conceptual diagram of a computing system performing anexample process 200 of transcribing a voice input 210 to text using abiased language model 228. The process 200 is similar to the process 100of FIG. 1, but in the process 200 dialog state history data is used atleast in part to determine a dialog state that corresponds to the voiceinput 210. Generally, dialog state history data identifies one or moredialog states that have previously occurred in a dialog session of agiven user. In some cases, dialog state history data may identify adialog state that immediately preceded the dialog state for a newtranscription request. The speech recognizer 102 can then evaluate adialog state-flow model to predict the dialog state for a newtranscription request based on the indication of which dialog stateimmediately preceded the voice input for the new request. In someimplementations, as described in the following paragraphs, dialog statehistory data may be used alone (i.e., without other context data) todetermine the dialog state associated with a transcription request. Insome implementations, multiple signals, including from both context dataand dialog state history data, may be used together by the speechrecognizer 102 to determine the dialog state associated with atranscription request.

At operation A (204), the user's device 208 generates a transcriptionrequest 212 and transmits the request 212 to the speech recognizer 202.The request 212 includes audio data that characterizes the voice input210 detected by the device 208. In this example, the voice input 210 isa recording of the user's utterance “pepperoni and mushroom.” Therequest 212 may or may not include other data usable by the speechrecognizer 202 to transcribe the voice input 210. In someimplementations, the request 212 may further include an applicationidentifier, a dialog identifier, a dialog state identifier, othercontext data, dialog state history data, a session identifier, or acombination of two or more of these. In some implementations, therequest 212 may include dialog state history data that identifies thelast n dialog states that have occurred in the dialog session. Thespeech recognizer 202 may make dialog state history data available tothe user device 208 by exposing an application programming interface(API) to the device 208 or by providing an indication of the dialogstate identifier that corresponds to a given request to the user device208 along with the transcription result 230 that request. For example,the user device 208 may submit a first transcription request to thespeech recognizer 202, and in response, the speech recognizer 202provides to the user device 208 a transcription result and the dialogstate identifier associated with the first request. Subsequently, theuser device 208 may submit a second transcription request to the speechrecognizer 202 that includes, as part of dialog state history data, thedialog state identifier associated with the first (preceding) request.The dialog state identifier associated with the first request can thenbe used by the speech recognizer 202, along with a dialog state-flowmodel, to determine a dialog state associated with the second request,as further described below.

In some implementations, the request 212 may include a dialog sessionidentifier in addition to or alternatively to dialog state history data.The dialog session identifier is data that indicates a particular dialogsession associated with the request 212. The dialog session identifiermay be used by the speech recognizer 202 to correlate a series oftranscription requests that relate to a same dialog session. Forexample, a first transcription request that includes a dialog sessionidentifier may be sent from the user device 208 to the speech recognizer202. The speech recognizer 202 may determine a dialog state associatedwith the first transcription request and may store a record thatassociates the determined dialog state with the session identifier. Whenthe speech recognizer 202 later receives a second transcription requestthat includes the same session identifier, the speech recognizer 202 canaccess the stored record to identify the preceding dialog state that wasassociated with the first request. Based on the preceding dialog stateand a dialog state-flow model, the speech recognizer 202 can determinethe dialog state associated with the second request and store a recordthat correlates the second dialog state with the session identifier. Thespeech recognizer 202 can continue this process to successivelydetermine subsequent dialog states for subsequent transcription requestsbased on preceding dialog states in a same session.

At operation B (214), upon receiving the request 212, the speechrecognizer 202 identifies the dialog state that the speech recognizer202 determined as being associated with the last transcription requestthat was received from the user device 208 for the same dialog session.For example, in completing a pizza order, the user 206 may provide asuccession of voice inputs such as “carryout,” then “thin crust,” andthen “pepperoni and mushroom,” which are provided in successivetranscription requests to the speech recognizer 202. In response toreceiving the third request 212, the speech recognizer 202 may identifythat the dialog state associated with the preceding request in the samedialog session as dialog state ‘2’ (highlighted in chart 216). In someimplementations, the speech recognizer 202 may determine the precedingdialog session by correlating a dialog session identifier included inthe request 212 with information stored by the speech recognizer 202that indicates the last one or more dialog states determined for thesame dialog session. In some implementations, the speech recognizer 202may determine the preceding dialog state based on dialog state historydata contained in the request 212 that directly identifies the precedingstate.

At operation C (218), the speech recognizer 202 determines the dialogstate that is most likely associated with the transcription request 212(and thus most likely associated with the voice input 110 included inthe request 212). In some implementations, the dialog state can bedetermined based on the one or more preceding dialog states that wereidentified at operation B (214) and a dialog state-flow model. A dialogstate-flow model generally indicates a sequence of dialog states thatare expected to occur in a given dialog, and is described with here withreference to FIG. 3.

FIG. 3 depicts a conceptual representation of an example dialogstate-flow model. The dialog state-flow model is represented as a graph300 that includes a plurality of nodes 302 a-g and a plurality of edges304 a-l that connect different ones of the nodes 302 a-g. Eachrespective dialog state in the dialog represented by the model isrepresented by a respective node 302 a-g in the graph 300. The edges 304a-l represent candidate transitions between dialog states. For example,the node 302 a (representing a first dialog state) has two outboundarrows 304 a and 304 b that point to nodes 302 b (representing a seconddialog state) and 302 c (representing a third dialog state),respectively. Thus, according to the model, it is possible that thedialog state that follows the first dialog state 302 a may be either thesecond dialog state 302 b or the third dialog state 302 c. However,because no edges point from the node 302 a for the first dialog state tothe respective nodes for the fourth, fifth, sixth, or seventh dialogstates (302 d-g), it may not be possible for the dialog to flow from thefirst dialog state to these other dialog states.

In some implementations, the dialog state-flow model may assignprobabilities to the transitions among each pair of dialog statesrepresented in the model. For example, the model indicates that there isan equal probability of either the second or third dialog states 302 a,302 b following the first dialog state 302 a. However, the likelihood ofthe dialog returning to the first dialog state 302 a immediately afterthe fourth dialog state 302 d is only forty percent, whereas thelikelihood that the dialog would proceed from the fourth dialog state302 d to the seventh dialog state 302 g is sixty percent. In someimplementations, the dialog state-flow model can be automaticallylearned by the speech recognizer or another computing system based onanalyses of the sequences of dialog states that occurred across manydialog sessions from one or more user devices over time. In someimplementations, the dialog state-flow model may be manually defined bya user, such as an application developer that developed a given dialog.In some implementations, a speech recognizer may be capable of accessingand using respective models for each of a plurality of dialogs.

Referring again to FIG. 2 and the discussion of operation C (218), adialog state may, in some implementations, be determined for the voiceinput 210 (and request 212) based on respective scores that aredetermined for a set of dialog states that indicate the likelihood ofeach respective dialog state matching the request 212 or voice input210. Example scores for the set of five dialog states associated withthe pizza ordering dialog are shown in table 220. In someimplementations, the speech recognizer 202 selects the dialog state thathas the highest probability score. In the example of FIG. 2, dialogstate ‘3’, which corresponds to the pizza toppings selection stage ofthe dialog, has the highest probability score and is determined to bethe dialog state that corresponds to transcription request 212.

In some implementations, the dialog state probability scores may furtherbe based on context data associated with the request 212. The speechrecognizer 202 may compare context data included in the request 212 withrespective context data associated with each of the dialog states todetermine a respective context similarity score for each of the dialogstates. Generally, a higher context similarity score indicates a closermatch between the context data in the request 212 and the context dataassociated with a given dialog state. In some implementations, thecontext similarity score can be based on a weighted combination ofsimilarity scores among multiple types of context data, such as userinterface hashes, location data, and user profile data. In someimplementations, the final probability score assigned to each of thedialog states (shown, for example, in the far-right column of table 220)can be based on a weighted combination of the context similarity scoreand a sequence score. The sequence score may be derived from theprobabilities in a dialog state-flow model and may indicate theprobability of a dialog state given one or more preceding dialog states.

At operations D (222), E (226), and F (232), the process 200 proceeds ina manner similar to operations C (118), D (124), and E (128) of theprocess 100 depicted in FIG. 1. In particular, at operation D (222), thelanguage model 228 is biased based on the set of n-grams associated withthe dialog state that was selected during operation C (218). Atoperation E (226), the speech recognizer 202 generates a transcriptionresult 230 of the voice input 110 using the biased language model 228.Finally, at operation F (232), the transcription result 230 is servedfrom the speech recognizer 202 to the user device 208. In someimplementations, the transcriptions result 230 can be served to thedevice 208 in conjunction with a dialog state identifier, which thedevice 208 may include in a subsequent transcription request in a dialogsession for use by the speech recognizer 202 to determine the nextdialog state.

Referring now to FIG. 4, a flowchart is shown of an example process 400for analyzing transcriptions of voice inputs to determine dialog statesin a multi-interaction voice dialog. In some implementations, arespective set of n-grams may be assigned to each of the dialog statesand these n-gram sets may later be used by a speech recognizer atruntime to bias a language model. For example, probability dataassociated with the n-grams for a given dialog state may be adjusted ina language model responsive to a determination that a voice inputcorresponds to the given dialog state. In some implementations, theprocess 400 may be employed by a speech recognition system toautomatically learn dialog states for a dialog and to automaticallylearn how to bias a language model for each dialog state. Accordingly,in some implementations, an application that uses a speech recognitionservice of the speech recognition system need not keep track of the flowof dialog states during a given series of voice interactions with auser, and need not explicitly inform the speech recognition system ofthe dialog state that a given transcription request corresponds to, theset of n-grams that are to be used in biasing a language model for agiven transcription request, or both.

At stage 402, a computing system receives audio data that indicatesvoice inputs of users from a plurality of computing devices. The voiceinputs are generally utterances spoken by users as part of a dialog. Foreach user, the dialog may include a series of voice inputs that relateto a particular activity. For example, the dialog for an appointmentscheduling activity may include respective voice inputs that identifythe starting time, duration, location, description, and invitees of anappointment. In some cases, users may provide input for all availableappointment scheduling parameters. In other cases, users may provideinput for only a portion of the available appointment schedulingparameters. Additionally, the order that the parameters are provided invoice inputs may vary among users. Thus, even though the voice inputsmay all pertain to dialogs for a same activity (e.g., appointmentscheduling), the number and sequence of voice inputs may vary acrossdialog sessions. In some implementations, the computing system mayreceive voice inputs that correspond to multiple different dialogs.Because the process 400 generally relates to determining the dialogstates and n-gram sets for a particular dialog (e.g., appointmentscheduling), the system may filter the received data to include onlydata for voice inputs that correspond to that dialog. Data for voiceinputs that correspond to other dialogs (e.g., pizza ordering, financialtransactions, social media posting) may be discarded.

At stage 404, the computing system optionally identifies context dataassociated with the received voice inputs. In some implementations, thecontext data may be provided by user devices in transcription requeststo the computing system. The transcription requests may also include theaudio data for the voice inputs that are requested to be transcribed.Context data generally includes any data (other than voice input audiodata) that the speech recognizer is capable of using to determine atranscription of the voice input. For example, a user device may computea screen signature that characterizes the display of a user interface onthe device at or near the time the device detects a voice input. Thescreen signature may in some instances be a hash value determined basedon values associated with user interface elements that were displayed bya device at or near the time the device detects a voice input. Thescreen signature (or other individual pieces of context data) may or maynot be sufficient for the computing system to determine a dialog stateassociated with a voice input. In some implementations, a given voiceinput can be associated with a single piece of context data (e.g., ascreen signature). In some implementations, a voice input can beassociated with multiple pieces of context data (e.g., a screensignature and a dialog hint). A dialog hint is a type of context datathat indicates the user device's estimated dialog state. If the userdevice reliably keeps track of dialog states during a dialog, then thedialog hint may effectively serve as a dialog state identifier. If theuser device does not reliably keep track of dialog states, then thecomputing system may afford the dialog hint less weight in determining adialog state associated with the user device. In some implementations,the computing system may not identify context data associated with thereceived voice inputs and may determine dialog states and n-grams setswithout context data.

At stage 406, the system determines transcriptions of the received voiceinputs (or at least of the voice inputs that have been filtered foranalysis). The transcriptions may be determined by a speech recognizerthat converts voice inputs to text. The speech recognizer may include acollection of components that enable the conversion of audio data forthe voice inputs to text. A language model may be included among thesecomponents, which is generally configured to determine probabilities ofsequences of terms in a language. The language model may evaluatecandidate sequences of terms for a transcription and select a mostprobable sequence of terms as the transcription that is ultimatelyprovided as output by the speech recognizer. In some implementations, ageneral, unbiased language model may be used to determine transcriptionsof the voice inputs during stage 406 since the dialog states andlanguage model biasing data (e.g., n-grams sets) may not yet have beendetermined by this stage of the process 400. In some implementations,the computing system may simply obtain transcriptions of voice inputsthat were determined by one or more other computing systems withoutitself needing to receive the audio data of the voice inputs andgenerating the transcriptions as part of the process 400.

At stage 408, the computing system analyzes the transcriptions of thevoice inputs to identify respective sets of one or more n-grams thatoccur in each of at least some of the transcriptions. The respective setof n-grams identified for each transcription may be provided in a vectorthat represents the transcription. The vector may indicate therespective set of n-grams identified for each transcription withoutregard to the order that the n-grams occurred in the transcription. Insome implementations, every n-gram that occurs in a transcription may beidentified and added to the corresponding vector for that transcription.In some implementations, only a proper subset of all the n-grams thatoccur in a transcription may be identified and added to thecorresponding vector for that transcription. The subset of n-grams maybe selected, for example, based on prominence scores associated with then-grams. For example, n-grams that occur less frequently in a languagemay be assigned a higher prominence score, while n-grams that occur morefrequently in a language (e.g., pronouns, articles, common adjectivesand nouns) may be assigned a lower prominence score. N-grams that areassigned prominence scores that exceed a threshold score may be selectedfor inclusion in the transcription's vector, for example, or the n-gramshaving the top n prominence scores in a transcription may be selected(where n is a predefined integer such as 1, 2, 3, 4, or more).

At stage 410, the computing system generates groups of transcriptionsbased on similarities among the transcriptions. Notably, thisdescription refers to groups of transcriptions by way of example only.Because each transcription corresponds to just a single voice input anda single set of n-grams identified as occurring in the transcription,the computing system could equally generate groups of voice inputs orgroups of n-gram sets based on similar techniques to those describedherein for generating groups of transcriptions. The discussion hererelating to groups of transcriptions thus applies to these other typesof groups as well.

In some implementations, the transcriptions may be grouped based onsemantic similarities of n-grams occurring in the transcriptions. Forexample, in determining groups of transcriptions of voice inputs to anappointment scheduling application, a first group of transcriptions maybe formed among transcriptions having n-grams relating to appointmenttimes (e.g., “noon,” “12 pm,” “8:30 am,” “in the evening,” “4 pm”); asecond group of transcriptions may be formed among transcriptions havingn-grams relating to appointment locations (e.g., “conference room,”“coffee shop,” “downtown,” “office,” “avenue,” “street,” “floor,”“suite”); and a third group of transcriptions may be formed amongtranscriptions having n-grams relating to appointment descriptions(e.g., “meeting,” “lunch,” “teleconference,” “review,” “party”). In someimplementations, the semantic similarities of transcriptions may bedetermined by identifying one or more topics associated with the n-gramsin a given transcription. The topics may be identified by a named-entityrecognition engine, for example, that associates n-grams with topics andthat can label text samples with topics based on the n-grams found inthe text samples. Once the topics are determined, transcriptions thatrelate to one or more same topics may be grouped. In someimplementations transcriptions that relate to topics that are differentbut similar may be grouped.

In some implementations, the transcriptions may be grouped based onsimilarities among the identified context data associated with the voiceinputs from which the transcriptions were derived. For example, a firstgroup of transcriptions may be formed among transcriptions of voiceinputs having a first screen signature, a second group of transcriptionsmay be formed among transcriptions of voice inputs having a secondscreen signature, and so on. In another example, a first group oftranscriptions may be formed among transcriptions of voice inputs spokenat times within a first time period (e.g., 8 AM-12 PM), a second groupof transcriptions may be formed among transcriptions of voice inputsspoken at times within a second time period (e.g., 12:01 PM-4 PM), andso on. Groups may be also be formed based on other types of matching orsimilar context data, such as location data, user profile data, userdemographic data, dialog hints, or indications of one or moreapplications running on a device when the spoken input was detected, forexample. In some implementations, transcriptions may be grouped based onsimilarities among multiple types of context associated with the voiceinputs from which the transcriptions were derived. For example, groupsof transcriptions may be formed among transcriptions of voice inputshaving similarities in both screen signatures and periods of time inwhich the voice inputs were detected at a user device. In someimplementations, different types of context data may be weightedrelative to each other such that similarities among certain types ofcontext are more likely to impact groupings than other types of context.

In some implementations, the groups of transcriptions may be generatedbased on sematic similarities of n-grams occurring in thetranscriptions, and not based on context data associated with the voiceinputs from which the transcriptions were derived. In someimplementations, the groups of transcriptions may be generated based oncontext data associated with the voice inputs from which thetranscriptions were derived, and not based on semantic similarities ofn-grams occurring in the transcriptions. However, in someimplementations, the groups of transcriptions may be generated based onboth (i) semantic similarities of n-grams occurring in thetranscriptions and (ii) context data associated with the voice inputsfrom which the transcriptions were derived. In the latterimplementations, transcriptions that are both semantically similar andthat have similar context data may be grouped together, for example.Thus, transcriptions having n-grams that are only slightly similarsemantically may be grouped if their contexts are very similar, andtranscriptions having context that are only slightly similar may begrouped if they are highly semantically related.

In some implementations, after the computing system generates an initialset of groups of transcriptions, groups that are determined to besimilar may be merged to reduce the overall number of groups oftranscriptions. The final set of transcription groups generated by thecomputing system correspond to respective dialog states that aredetermined to occur in a dialog. Since each dialog state may be used bya speech recognizer to bias a language model differently, consolidatinggroups to reduce the number of dialog states that are detectable by thespeech recognizer may be beneficial. In particular, merging groups caneliminate redundant groups and increases separation among the groups(and, thus diversity among the dialog states) to ensure meaningfuldifferences in how a language model is biased as between each of thedialog states. For example, a first stage of a dialog may solicit users'voice inputs for appointment starting times, a second stage of a dialogmay solicit users' voice inputs for appointment ending times, and athird stage of a dialog may solicit users' voice inputs for a number ofattendees to the appointment. Because there may be substantial overlapamong n-grams in the voice inputs at each of these stages (e.g.,statement of numbers and times), the transcriptions of the voice inputsmay be merged into a single group. The determined dialog state thatresults from the merged group may thus correspond to three separatestages of voice interactions because the same set of n-grams may be usedto effectively bias a language model in a same way for each of thesestages.

The computing system may identify groups of transcriptions to mergeaccording to various techniques. In some implementations, a set ofn-grams from each group may be compared to a respective set of n-gramsfrom each other group, and similarity scores between the sets of n-gramsof each pair of groups can be determined based on the comparisons. Ifthe similarity score between the n-grams in a given pair of groupssatisfies (e.g., exceeds) a threshold similarity score, then the groupsmay be merged. A result of the merger can be a group that includes allor at least some of the transcriptions from each of the merged groups.The similarity score may be determined, for example, based on a numberor frequency of matches between n-grams of the groups being compared.For example, if an initial context-based grouping of transcriptionsresulted in a first group for a first screen signature value and asecond group for a second screen signature value, but the transcriptionsof voice inputs among each of the groups are largely the same, thegroups may be merged into a single group in the final set of groupsgenerated by the computing system. In some implementations, groups maybe merged in successive iterations until a limit is reached (e.g., untila predetermined number of iterations have been completed, until none ofthe similarity scores between the groups satisfies the thresholdsimilarity score, until the number of groups remaining does not exceed apredetermined maximum number of groups, or a combination of these). Insome implementations, the similarity score between groups oftranscriptions may be determined by taking the cosine distance betweenthe respective sets of n-grams from each of the groups. The cosinedistance may be calculated by generating vectors of n-grams from eachgroup (e.g., according to a bag-of-words technique), and determining thedistance among the vectors. In some implementations, the similarityscore between groups of transcriptions may be determined by taking thesets of n-grams to a low-dimensional space and determining a similarityin the low-dimensional space.

FIGS. 5A and 5B depict conceptual diagrams of techniques for mergingsimilar groups of transcriptions to form a final set of groups thatcorrespond to dialog states determined to occur in a dialog.

In FIG. 5A, initial groups of transcriptions 504, 506, and 510 aregrouped based on the semantic similarity of terms (n-grams) in thetranscriptions. This type of grouping may be beneficial, for example,when context data is unavailable or where the speech recognizer isconfigured to use a dialog state-flow model, rather than context data,to detect dialog states of voice input transcription requests atruntime. After the initial groups 504, 506, and 510 are generated, twoof the groups 504 and 506 are determined to contain similar sets ofn-grams and are therefore merged into a single group 502. The mergedgroup 502 and the third initial group 510 are then correlated torespective dialog states 508 and 512 in a given dialog.

In FIG. 5B, initial groups of transcriptions 552, 556, and 558 aregrouped based on context data associated with the transcriptions (andthus associated with the voice inputs from which the transcriptions weredetermined). Contextual grouping may be beneficial, for example, whencontext data has a strong correlation to dialog states will be availableto a speech recognizer to transcribe voice inputs during runtime. Insome implementations, dialog states determined based on context mayobviate any need for a speech recognizer to determine dialog statesbased on dialog state history data or a dialog state-flow model, forexample. After the initial groups 552, 556, and 558 are generated, twoof the groups 556 and 558 are determined to contain similar sets ofn-grams and are therefore merged into a single group 554. The mergedgroup 554 and the first initial group 552 are then correlated torespective dialog states 560 and 562 in a given dialog.

Referring again to FIG. 4, at stage 414 the process 400 assigns, to eachof the dialog states determined at stages 410 and 412, a respective setof n-grams for a speech recognizer to use in biasing a language modelwhen transcribing a voice input that corresponds to the respectivedialog state. In some implementations, the set of n-grams assigned to agiven dialog state can be selected from among all the n-grams that occurin the transcriptions that comprise the group corresponding to the givendialog state. In some implementations, a count of a number of times thateach n-gram occurs in the group of transcriptions can be determined, andthe most frequently occurring n-grams may be selected based on thecounts (e.g., n-grams having counts that satisfy a threshold count maybe selected and/or a predetermined number of n-grams having the highestcounts may be selected). In some implementations, the selected n-gramsmay be selected from among a filtered set of n-grams that, for example,excludes insignificant terms (e.g., “of,” “the,” “a,” “to,” “for,”etc.). The selected sets of n-grams can be stored in association withtheir respective dialog states.

In some implementations, where the groups of transcriptions have beencreated based at least in part on context data associated with thetranscriptions, at stage 416 the computing system may assign, to each ofthe dialog states determined at stages 410 and 412, a respective set ofcontext data that may be used by a speech recognizer to associate agiven voice input or transcription request with the respective dialogstate. The set of context data assigned to a given dialog state may beanalogized to a fingerprint that uniquely identifies the dialog state.Thus, when a speech recognizer receives a voice input transcriptionrequest that includes context data, the context data from the requestmay be compared to the respective sets of context data assigned to eachof the dialog states. If a match or strong correlation is determinedbetween the context data in the request and one of the assigned sets ofcontext data, then speech recognizer may identify that the requestpertains to the dialog state that corresponds to the matching set ofcontext data. In some implementations, the set of context data that thecomputing system assigns to a dialog state may be based on the contextdata associated with all or some of the transcriptions in the group thatcorresponds to the dialog state. For example, if a significant pluralityor a majority of the transcriptions in a given group are associated witha first screen signature value, then the first screen signature valuemay be assigned to the dialog state corresponding to that group.

In some implementations, the computing system at stage 418 can determinea dialog state-flow model that indicates sequences of dialog states thatare likely to occur in a dialog session. In some implementations, thedialog state flow model may indicate, for each dialog state determinedin stages 410 and 412, probabilities that one or more other dialogstates will be the next dialog state in a dialog session. For example,in the flow model depicted in FIG. 3, the probability of dialog state 7following dialog state 4 is 0.6 and the probability of dialog state 1following dialog state 4 is 0.4. The probabilities of any other dialogstates following dialog state 4 is zero. In some implementations, thecomputing system may determine the dialog state-flow model based onidentified sequences of dialog states that occurred in records ofhistorical dialog sessions. For example, if in the records of historicaldialog sessions a first dialog state was followed by a second dialogstate eighty-percent of the time and followed by a third dialog statetwenty-percent of the time, then a probability of 0.8 may be assigned inthe dialog state-flow model to the transition from the first dialogstate to the second dialog state and a probability of 0.2 may beassigned to the transition from the first dialog state to the thirddialog state.

FIG. 6 is a flowchart of an example process 600 for performing speechrecognition on a voice input using a biased language model that isselected based on a dialog state associated with the voice input. Insome implementations, the process 600 may be carried out by a speechrecognition computing system such as the speech recognizers described inFIGS. 1 and 2. The process 600 may also be performed using datadetermined in the process 400 of FIG. 4 about dialog states, n-grams,context data, and dialog state-flow models.

At stage 602, the speech recognition system receives a voice input thatis requested to be transcribed. In some implementations, the system atstage 602 also receives context data associated with the voice input.The context data can indicate a condition of a user device that detectedthe voice input at or near a time that the voice input was detected. Forexample, the context data may indicate a screen signature thatcharacterizes a display of the user device when the voice input wasdetected, a dialog hint, or combinations of these and other types ofcontext data.

At stage 606, the speech recognition system analyzes the voice input,the context data, or both to determine a dialog state for the voiceinput. In some implementations, the dialog state can be determined bymatching context data in a transcription request to a particular set ofcontext data that has been stored and correlated with the correspondingdialog state (stage 608). In some implementations, the dialog state canbe determined based on dialog state history data and a dialog state-flowmodel that predicts sequences of dialog states. The dialog state historydata may indicate one or more dialog states that preceded the dialogstate for the current transcription request, and may be pre-stored bythe speech recognition system or may be the provided in a transcriptionrequest from a user device.

At stage 612, the speech recognition system identifies a set of n-gramsthat have been assigned to the dialog state that was determined at stage606. At stage 614, the identified set of n-grams are applied to bias alanguage model. For example, probabilities associated with n-grams inthe identified set of n-grams may be increased in the language model tomake the language model more likely to select the assigned n-grams. Insome implementations, the language model may be biased after the voiceinput is received and the dialog state for the voice input determined.In some implementations, the speech recognition system may generatebiased language models for each of the dialog states before a voiceinput is received. Later, when a request to transcribe a voice input isreceived, the speech system may access the pre-biased language modelcorresponding to the dialog state for the voice input. At stage 616, thevoice input can be transcribed to text using the biased language model.The transcribed text can then be transmitted to the computing devicethat requested the transcription.

FIG. 7 shows an example of a computing device 700 and a mobile computingdevice that may be used to implement the computer-implemented methodsand other techniques described herein. The computing device 700 isintended to represent various forms of digital computers, such aslaptops, desktops, workstations, personal digital assistants, servers,blade servers, mainframes, and other appropriate computers. The mobilecomputing device is intended to represent various forms of mobiledevices, such as personal digital assistants, cellular telephones,smart-phones, and other similar computing devices. The components shownhere, their connections and relationships, and their functions, aremeant to be exemplary only, and are not meant to limit implementationsof the inventions described and/or claimed in this document.

The computing device 700 includes a processor 702, a memory 704, astorage device 706, a high-speed interface 708 connecting to the memory704 and multiple high-speed expansion ports 710, and a low-speedinterface 712 connecting to a low-speed expansion port 714 and thestorage device 706. Each of the processor 702, the memory 704, thestorage device 706, the high-speed interface 708, the high-speedexpansion ports 710, and the low-speed interface 712, are interconnectedusing various busses, and may be mounted on a common motherboard or inother manners as appropriate. The processor 702 can process instructionsfor execution within the computing device 700, including instructionsstored in the memory 704 or on the storage device 706 to displaygraphical information for a GUI on an external input/output device, suchas a display 716 coupled to the high-speed interface 708. In otherimplementations, multiple processors and/or multiple buses may be used,as appropriate, along with multiple memories and types of memory. Also,multiple computing devices may be connected, with each device providingportions of the necessary operations (e.g., as a server bank, a group ofblade servers, or a multi-processor system).

The memory 704 stores information within the computing device 700. Insome implementations, the memory 704 is a volatile memory unit or units.In some implementations, the memory 704 is a non-volatile memory unit orunits. The memory 704 may also be another form of computer-readablemedium, such as a magnetic or optical disk.

The storage device 706 is capable of providing mass storage for thecomputing device 700. In some implementations, the storage device 706may be or contain a computer-readable medium, such as a floppy diskdevice, a hard disk device, an optical disk device, or a tape device, aflash memory or other similar solid state memory device, or an array ofdevices, including devices in a storage area network or otherconfigurations. The computer program product may also containinstructions that, when executed, perform one or more methods, such asthose described above. The computer program product can also be tangiblyembodied in a computer- or machine-readable medium, such as the memory704, the storage device 706, or memory on the processor 702.

The high-speed interface 708 manages bandwidth-intensive operations forthe computing device 700, while the low-speed interface 712 manageslower bandwidth-intensive operations. Such allocation of functions isexemplary only. In some implementations, the high-speed interface 708 iscoupled to the memory 704, the display 716 (e.g., through a graphicsprocessor or accelerator), and to the high-speed expansion ports 710,which may accept various expansion cards (not shown). In theimplementation, the low-speed interface 712 is coupled to the storagedevice 706 and the low-speed expansion port 714. The low-speed expansionport 714, which may include various communication ports (e.g., USB,Bluetooth, Ethernet, wireless Ethernet) may be coupled to one or moreinput/output devices, such as a keyboard, a pointing device, a scanner,or a networking device such as a switch or router, e.g., through anetwork adapter.

The computing device 700 may be implemented in a number of differentforms, as shown in the figure. For example, it may be implemented as astandard server 720, or multiple times in a group of such servers. Inaddition, it may be implemented in a personal computer such as a laptopcomputer 722. It may also be implemented as part of a rack server system724. Alternatively, components from the computing device 700 may becombined with other components in a mobile device (not shown), such as amobile computing device 750. Each of such devices may contain one ormore of the computing device 700 and the mobile computing device 750,and an entire system may be made up of multiple computing devicescommunicating with each other.

The mobile computing device 750 includes a processor 752, a memory 764,an input/output device such as a display 754, a communication interface766, and a transceiver 768, among other components. The mobile computingdevice 750 may also be provided with a storage device, such as amicro-drive or other device, to provide additional storage. Each of theprocessor 752, the memory 764, the display 754, the communicationinterface 766, and the transceiver 768, are interconnected using variousbuses, and several of the components may be mounted on a commonmotherboard or in other manners as appropriate.

The processor 752 can execute instructions within the mobile computingdevice 750, including instructions stored in the memory 764. Theprocessor 752 may be implemented as a chipset of chips that includeseparate and multiple analog and digital processors. The processor 752may provide, for example, for coordination of the other components ofthe mobile computing device 750, such as control of user interfaces,applications run by the mobile computing device 750, and wirelesscommunication by the mobile computing device 750.

The processor 752 may communicate with a user through a controlinterface 758 and a display interface 756 coupled to the display 754.The display 754 may be, for example, a TFT (Thin-Film-Transistor LiquidCrystal Display) display or an OLED (Organic Light Emitting Diode)display, or other appropriate display technology. The display interface756 may comprise appropriate circuitry for driving the display 754 topresent graphical and other information to a user. The control interface758 may receive commands from a user and convert them for submission tothe processor 752. In addition, an external interface 762 may providecommunication with the processor 752, so as to enable near areacommunication of the mobile computing device 750 with other devices. Theexternal interface 762 may provide, for example, for wired communicationin some implementations, or for wireless communication in otherimplementations, and multiple interfaces may also be used.

The memory 764 stores information within the mobile computing device750. The memory 764 can be implemented as one or more of acomputer-readable medium or media, a volatile memory unit or units, or anon-volatile memory unit or units. An expansion memory 774 may also beprovided and connected to the mobile computing device 750 through anexpansion interface 772, which may include, for example, a SIMM (SingleIn Line Memory Module) card interface. The expansion memory 774 mayprovide extra storage space for the mobile computing device 750, or mayalso store applications or other information for the mobile computingdevice 750. Specifically, the expansion memory 774 may includeinstructions to carry out or supplement the processes described above,and may include secure information also. Thus, for example, theexpansion memory 774 may be provide as a security module for the mobilecomputing device 750, and may be programmed with instructions thatpermit secure use of the mobile computing device 750. In addition,secure applications may be provided via the SIMM cards, along withadditional information, such as placing identifying information on theSIMM card in a non-hackable manner.

The memory may include, for example, flash memory and/or NVRAM memory(non-volatile random access memory), as discussed below. The computerprogram product contains instructions that, when executed, perform oneor more methods, such as those described above. The computer programproduct can be a computer- or machine-readable medium, such as thememory 764, the expansion memory 774, or memory on the processor 752. Insome implementations, the computer program product can be received in apropagated signal, for example, over the transceiver 768 or the externalinterface 762.

The mobile computing device 750 may communicate wirelessly through thecommunication interface 766, which may include digital signal processingcircuitry where necessary. The communication interface 766 may providefor communications under various modes or protocols, such as GSM voicecalls (Global System for Mobile communications), SMS (Short MessageService), EMS (Enhanced Messaging Service), or MMS messaging (MultimediaMessaging Service), CDMA (code division multiple access), TDMA (timedivision multiple access), PDC (Personal Digital Cellular), WCDMA(Wideband Code Division Multiple Access), CDMA2000, or GPRS (GeneralPacket Radio Service), among others. Such communication may occur, forexample, through the transceiver 768 using a radio-frequency. Inaddition, short-range communication may occur, such as using aBluetooth, WiFi, or other such transceiver (not shown). In addition, aGPS (Global Positioning System) receiver module 770 may provideadditional navigation- and location-related wireless data to the mobilecomputing device 750, which may be used as appropriate by applicationsrunning on the mobile computing device 750.

The mobile computing device 750 may also communicate audibly using anaudio codec 760, which may receive spoken information from a user andconvert it to usable digital information. The audio codec 760 maylikewise generate audible sound for a user, such as through a speaker,e.g., in a handset of the mobile computing device 750. Such sound mayinclude sound from voice telephone calls, may include recorded sound(e.g., voice messages, music files, etc.) and may also include soundgenerated by applications operating on the mobile computing device 750.

The mobile computing device 750 may be implemented in a number ofdifferent forms, as shown in the figure. For example, it may beimplemented as a cellular telephone 780. It may also be implemented aspart of a smart-phone 782, personal digital assistant, or other similarmobile device.

Various implementations of the systems and techniques described here canbe realized in digital electronic circuitry, integrated circuitry,specially designed ASICs (application specific integrated circuits),computer hardware, firmware, software, and/or combinations thereof.These various implementations can include implementation in one or morecomputer programs that are executable and/or interpretable on aprogrammable system including at least one programmable processor, whichmay be special or general purpose, coupled to receive data andinstructions from, and to transmit data and instructions to, a storagesystem, at least one input device, and at least one output device.

These computer programs (also known as programs, software, softwareapplications or code) include machine instructions for a programmableprocessor, and can be implemented in a high-level procedural and/orobject-oriented programming language, and/or in assembly/machinelanguage. As used herein, the terms machine-readable medium andcomputer-readable medium refer to any computer program product,apparatus and/or device (e.g., magnetic discs, optical disks, memory,Programmable Logic Devices (PLDs)) used to provide machine instructionsand/or data to a programmable processor, including a machine-readablemedium that receives machine instructions as a machine-readable signal.The term machine-readable signal refers to any signal used to providemachine instructions and/or data to a programmable processor.

To provide for interaction with a user, the systems and techniquesdescribed here can be implemented on a computer having a display device(e.g., a CRT (cathode ray tube) or LCD (liquid crystal display) monitor)for displaying information to the user and a keyboard and a pointingdevice (e.g., a mouse or a trackball) by which the user can provideinput to the computer. Other kinds of devices can be used to provide forinteraction with a user as well; for example, feedback provided to theuser can be any form of sensory feedback (e.g., visual feedback,auditory feedback, or tactile feedback); and input from the user can bereceived in any form, including acoustic, speech, or tactile input.

The systems and techniques described here can be implemented in acomputing system that includes a back end component (e.g., as a dataserver), or that includes a middleware component (e.g., an applicationserver), or that includes a front end component (e.g., a client computerhaving a graphical user interface or a Web browser through which a usercan interact with an implementation of the systems and techniquesdescribed here), or any combination of such back end, middleware, orfront end components. The components of the system can be interconnectedby any form or medium of digital data communication (e.g., acommunication network). Examples of communication networks include alocal area network (LAN), a wide area network (WAN), and the Internet.

The computing system can include clients and servers. A client andserver are generally remote from each other and typically interactthrough a communication network. The relationship of client and serverarises by virtue of computer programs running on the respectivecomputers and having a client-server relationship to each other.

In situations in which the systems, methods, devices, and othertechniques here collect personal information (e.g., context data) aboutusers, or may make use of personal information, the users may beprovided with an opportunity to control whether programs or featurescollect user information (e.g., information about a user's socialnetwork, social actions or activities, profession, a user's preferences,or a user's current location), or to control whether and/or how toreceive content from the content server that may be more relevant to theuser. In addition, certain data may be treated in one or more waysbefore it is stored or used, so that personally identifiable informationis removed. For example, a user's identity may be treated so that nopersonally identifiable information can be determined for the user, or auser's geographic location may be generalized where location informationis obtained (such as to a city, ZIP code, or state level), so that aparticular location of a user cannot be determined. Thus, the user mayhave control over how information is collected about the user and usedby a content server.

Although various implementations have been described in detail above,other modifications are possible. In addition, the logic flows depictedin the figures do not require the particular order shown, or sequentialorder, to achieve desirable results. In addition, other steps may beprovided, or steps may be eliminated, from the described flows, andother components may be added to, or removed from, the describedsystems. Accordingly, other implementations are within the scope of thefollowing claims.

1-20. (canceled)
 21. A computer-implemented method, comprising:receiving, by a computing device, audio data for a voice input to thecomputing device, wherein the voice input corresponds to an unknownstage of a multi-stage voice dialog between the computing device and auser of the computing device; determining, by the computing device, afirst prediction for the unknown stage of the multi-stage voice dialog;providing, by the computing device and to a voice dialog system, (i) theaudio data for the voice input to the computing device and (ii) anindication of the first prediction for the unknown stage of themulti-stage voice dialog; receiving, by the computing device and fromthe voice dialog system, a transcription of the voice input, wherein thetranscription was generated by processing the audio data with a modelthat was biased according to parameters that correspond to the firstprediction for the unknown stage of the multi-stage voice dialog orparameters that correspond to a second prediction for the unknown stageof the multi-stage voice dialog; and presenting the transcription of thevoice input with the computing device.
 22. The computer-implementedmethod of claim 21, wherein the transcription that is received from thevoice dialog system was generated by processing the audio data with amodel that was biased according to the parameters that correspond to thefirst prediction for the unknown stage of the multi-stage voice dialog.23. The computer-implemented method of claim 21, wherein thetranscription that is received from the voice dialog system wasgenerated by processing the audio data with a model that was biasedaccording to the parameters that correspond to the second prediction forthe unknown stage of the multi-stage voice dialog, wherein the secondprediction identifies a different stage of the multi-stage voice dialogthan a stage that is identified by the first prediction.
 24. Thecomputer-implemented method of claim 23, wherein the voice dialog systemgenerates the second prediction for the unknown stage of the multi-stagevoice dialog based on the first prediction and context data thatdescribes a context of the voice input to the computing device.
 25. Thecomputer-implemented method of claim 24, further comprising providing,by the computing device and to the voice dialog system in conjunctionwith the audio data for the voice input and the indication of the firstprediction, the context data that describes the context of the voiceinput to the computing device.
 26. The computer-implemented method ofclaim 24, wherein, in generating the second prediction for the unknownstage of the multi-stage voice dialog, the voice dialog system isconfigured to adjust a weight of the first prediction that wasdetermined by the computing device based on a confidence value assignedto the first prediction.
 27. The computer-implemented method of claim24, wherein the context data comprises a screen signature thatcharacterizes a state of a display of the computing device at a timewhen the voice input is received by the computing device.
 28. Thecomputer-implemented method of claim 21, wherein the first predictionfor the unknown stage of the multi-stage voice dialog represents anestimate of which stage from the multi-stage voice dialog that the voiceinput is directed to.
 29. The computer-implemented method of claim 21,wherein: the model comprises a language model; and the transcription wasgenerated by biasing the language model according to the parameters thatcorrespond to the first prediction for the unknown stage of themulti-stage voice dialog or the parameters that correspond to the secondprediction for the unknown stage of the multi-stage voice dialog. 30.The computer-implemented method of claim 29, wherein: biasing thelanguage model according to the parameters that correspond to the firstprediction comprises boosting probability scores in the language modelfor n-grams that are determined to frequently occur in voice inputscorresponding to a first stage of the multi-stage voice dialog that isidentified by the first prediction, and biasing the language modelaccording to the parameters that correspond to the second predictioncomprises boosting probability scores in the language model for n-gramsthat are determined to frequently occur in voice inputs corresponding toa second stage of the multi-stage voice dialog that is identified by thesecond prediction.
 31. The computer-implemented method of claim 21,wherein presenting the transcription of the voice input with thecomputing device comprises filling in a text field presented by thecomputing device with the transcription of the voice input.
 32. One ormore non-transitory computer-readable media having instructions storedthereon that, when executed by one or more processors of a computingdevice, cause the one or more processors to perform operationscomprising: receiving, by the computing device, audio data for a voiceinput to the computing device, wherein the voice input corresponds to anunknown stage of a multi-stage voice dialog between the computing deviceand a user of the computing device; determining, by the computingdevice, a first prediction for the unknown stage of the multi-stagevoice dialog; providing, by the computing device and to a voice dialogsystem, (i) the audio data for the voice input to the computing deviceand (ii) an indication of the first prediction for the unknown stage ofthe multi-stage voice dialog; receiving, by the computing device andfrom the voice dialog system, a transcription of the voice input,wherein the transcription was generated by processing the audio datawith a model that was biased according to parameters that correspond tothe first prediction for the unknown stage of the multi-stage voicedialog or parameters that correspond to a second prediction for theunknown stage of the multi-stage voice dialog; and presenting thetranscription of the voice input with the computing device.
 33. Thecomputer-readable media of claim 32, wherein the transcription that isreceived from the voice dialog system was generated by processing theaudio data with a model that was biased according to the parameters thatcorrespond to the first prediction for the unknown stage of themulti-stage voice dialog.
 34. The computer-readable media of claim 32,wherein the transcription that is received from the voice dialog systemwas generated by processing the audio data with a model that was biasedaccording to the parameters that correspond to the second prediction forthe unknown stage of the multi-stage voice dialog, wherein the secondprediction identifies a different stage of the multi-stage voice dialogthan a stage that is identified by the first prediction.
 35. Thecomputer-readable media of claim 34, wherein the voice dialog systemgenerates the second prediction for the unknown stage of the multi-stagevoice dialog based on the first prediction and context data thatdescribes a context of the voice input to the computing device.
 36. Thecomputer-readable media of claim 35, wherein the operations furthercomprise providing, by the computing device and to the voice dialogsystem in conjunction with the audio data for the voice input and theindication of the first prediction, the context data that describes thecontext of the voice input to the computing device.
 37. Thecomputer-readable media of claim 35, wherein, in generating the secondprediction for the unknown stage of the multi-stage voice dialog, thevoice dialog system is configured to adjust a weight of the firstprediction that was determined by the computing device based on aconfidence value assigned to the first prediction.
 38. Thecomputer-readable media of claim 35, wherein the context data comprisesa screen signature that characterizes a state of a display of thecomputing device at a time when the voice input is received by thecomputing device.
 39. The computer-readable media of claim 32, whereinthe first prediction for the unknown stage of the multi-stage voicedialog represents an estimate of which stage from the multi-stage voicedialog that the voice input is directed to.
 40. A computing devicecomprising: one or more processors; and one or more computer-readablemedia having instructions stored thereon that, when executed by the oneor more processors, cause performance of operations comprising:receiving, by the computing device, audio data for a voice input to thecomputing device, wherein the voice input corresponds to an unknownstage of a multi-stage voice dialog between the computing device and auser of the computing device; determining, by the computing device, afirst prediction for the unknown stage of the multi-stage voice dialog;providing, by the computing device and to a voice dialog system, (i) theaudio data for the voice input to the computing device and (ii) anindication of the first prediction for the unknown stage of themulti-stage voice dialog; receiving, by the computing device and fromthe voice dialog system, a transcription of the voice input, wherein thetranscription was generated by processing the audio data with a modelthat was biased according to parameters that correspond to the firstprediction for the unknown stage of the multi-stage voice dialog orparameters that correspond to a second prediction for the unknown stageof the multi-stage voice dialog; and presenting the transcription of thevoice input with the computing device.